This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-255630, filed Aug. 25, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus, mounted on a camera, for measuring the distance of an object and focusing the lenses on the object at the time of photographing the object. More specifically, the present invention relates to a focusing apparatus for appropriately measuring the distance of an object and focusing the lenses on the object even if an auxiliary light beam is emitted and a shadow is generated in a distance measurement range on a dark scene or the like.
2. Description of the Related Art
There is known hitherto a system of a focusing apparatus, mounted on a camera, for calculating the distance of an object and a focusing position by comparing two images of one object obtained through two optical paths. According to this system, in case of a dark scene or an object without a contrast, it sometimes occurs that clear image signals for distance measurement cannot be obtained and the object cannot be focused on. To prevent this, there is known a technique for applying auxiliary light beam from a light source, e.g., a strobe, to an object when distance measurement is carried out and for emphasizing image signals for the distance measurement.
FIG. 15 shows an example of the constitution of the appearance of an ordinary camera.
In FIG. 15, a pair of light receiving lenses 2R, 2L for distance measurement, a strobe section 3 and a photographic lens 4 are arranged in front of a body 1 of a camera 1. In addition, on the upper surface of the camera 1, there are arranged a release switch 6 and a display section (LCD) 5 indicating an operation mode and the number of frames of a film of the camera 1. During photographing, when a photographer operates the release button 6, strobe light is emitted and a distance is measured and exposure is carried out after focusing if an object (or a person) is dark. This strobe light is emitted as auxiliary light of a focusing distance measurement apparatus and as auxiliary light for exposure under the control of a control section provided in the camera 1.
FIG. 16 shows the positional relationship between an object and a camera in respect of distance measurement during photographing if the object and the camera are viewed from above. At the time of measuring a distance, if an object 20 is dark, strobe light is applied to the object 20 to illuminate the object 20. The illumination range is indicated by symbol xcex8. Reflected light from the face of the object 20 is passed through light receiving lenses 2R and 2L and incident on sensor arrays 7R and 7L, and a positional distance due to the parallax of the two lenses is accurately measured. At this time, an object distance is accurately measured under the principle of triangulation and accurate focusing is carried out.
In case of frequently employing auxiliary light during distance measurement, however, there are scenes to be noted. As shown in, for example, FIG. 17, if a wall 21 is present right in back of a principal object (or person) 20 and auxiliary light is emitted to carry out distance measurement, the distance of the object including a shadow part 22 generated by the auxiliary light is measured. This is because lenses 2R and 2L (or sensor arrays 7R and 7L) are disposed away from a strobe light emission section 3 by several centimeters on an ordinary camera. As a result, the shadow part 22 forming a large contrast image is erroneously focused on instead of the principal object in this distance measurement signal and the principal object 20 becomes disadvantageously out of focus.
It is an object of the present invention to provide a focusing apparatus capable of adjusting the focus of a camera on an object without the influence of a wall existing in the background while utilizing auxiliary light.
To attain this object, the present invention provides a focusing apparatus for focusing on an object based on object image signals outputted from a sensor, comprising: a light projection section projecting auxiliary light for focusing onto the object; a detection section detecting a signal corresponding to a shadow part of the object generated after projecting the auxiliary light among the object image signals outputted from the sensor when the auxiliary light is projected; and a control section conducting focusing control based on the object image signals outputted from the sensor when the auxiliary light is projected except for the image signal corresponding to the shadow part detected by the detection section.
According to the focusing apparatus constituted as stated above, the focusing auxiliary light is projected onto a dark object from the light projection section to detect the object image signals obtained by a plurality of optical paths in multiple-point distance measurement. Among the object image signals obtained from a pair of sensor arrays capturing reflected light of the auxiliary light, a part having a greater contrast than a preset contrast is determined as a shadow and focusing control is exercised using the object image signals of parts other than the part determined as a shadow by the control section.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.